Our Sun’s journey around the Milky Way’s galactic center puts it through some of the most complicated motions imaginable. Since time immemorial, astronomers and celestial mechanics have struggled to understand the how and why of our Star’s journey through the galactic disk.
But this American Museum of Natural History (AMNH) video below elegantly captures our own Sun’s motions through the galaxy and, in troubled times like these, is a needed reminder of nature’s reassuring order and structure.
Here are a few facts that you might not know about the Sun’s dynamics around the galaxy.
—- The Sun orbits the galactic center in a nearly circular orbit around the galactic center.
The Sun makes one orbit around the Milky Way roughly once every 225 million years and is thought to have made this journey some 20 times since its earliest days as a protostar.
We now know the orbital speed of the Sun in its Galactic orbit to better than two percent accuracy (or roughly 247 kilometers per second), Mark reid, an astronomer at the Harvard Smithsonian Center for Astrophysics, told me. The Sun is in a nearly circular orbit, with a slight ellipticity (of about five percent), he says.
On the largest scales, from great distances, the Milky Way would appear as a classic grand spiral galaxy, with four spiral arms. And our spot in the much ballyhooed suburbs of the galaxy’s disk isn’t a bad place to be. It’s far enough away from the chaotic galactic center, that it’s posited that things were quiet enough to allow for a solar system like ours to develop life at least once.
But as the Sun moves through the disk of the galaxy, it also encounters giant molecular clouds in which new stars are forming. These clouds can also alter the Sun’s orbit. And whether or not such encounters might periodically trigger an influx of comets influx from our outer solar system is still debated.
—- Recent estimates place the Sun an estimated 26,600 light years from the Milky Way’s galactic center.
Reid says astronomers primarily use two methods to determine the Sun’s distance to the galactic center. One involves infrared observations of stars that orbit the supermassive black hole dubbed Sagittarius A* (SGR A*) which lies in our Milky Way’s galactic center.
The other involves meticulous radio observations of this supermassive black hole in our galactic center. This method involves taking distance measurements of how SGR A* moves in comparison to background quasars that lie billions of light years away. This enables astronomers to accurately calculate the Sun’s distance from SGR A* with a great degree of precision.
—- The Sun is thought to have formed pretty near its current position
The Sun lies between two spiral arms Sagittarius and Perseus very close to a minor spur of the Milky Way known as the so-called Local Arm (or the Orion-Cygnus arm).
It’s hard to know how far the Sun has moved from the molecular cloud from which it formed since it has long been dispersed, astronomer Leo Blitz, a professor emeritus at the University of California, Berkeley, told me. But he still wonders whether we have always been at this distance from the galactic center.
Blitz says it’s possible that the Sun may have formed closer in towards the galactic center and over the eons migrated outward into our present location. As to why that might be? That’s in part because of random interactions with other stars.
—- The whole solar system is angled perpendicular to the plane of the galaxy.
The aforementioned Giant Molecular Clouds (GMCs) which pepper the plane of our galaxy have over time have also altered our solar system’s angle in relation to the galactic plane. Thus, the plane of our own solar system lies perpendicular to the galactic plane at an angle of some 60 percent. And that too is thought to be a dynamic number.
—- The Sun itself is bobbing up and down in a vertical motion in and out of midplane of our galactic disk almost like a cork in water.
Where are we now?
Although recent estimates put our position as some 81 light-years above the midplane of the galaxy, in fact, Reid puts that figure at only 20 light years above the plane.
Blitz says that once the Sun hits a height of some 300 light years above the galactic plane, it will begin its descent back down through the midplane, out the other side and then back up again. And our star’s journey up, down and around will continue just as it has for the last 4.6 billion years.